XS Plastic Mould Co., Ltd started to manufacture preform mould since 2009. With this long and rich experience in the preform moulds industrial, we can guarantee both good quality and competitve price.

• Preform design

Before we introduce preform mold, we need to understand why preform designed in that way. First is preform mouth. Every preform have mouth, as after stretch blow molding the preform mouth will become bottle mouth. Some full automatical stretch blow molding machine use mandrel to transport the preforms. In this case, we have to insure the preform neck with enough wall thickness to bear the mandrel plug in force. Lots of automatical stretch blow molding machine use gripper to transport preforms, so preforms need a space for gripper to hold them. Transport ring is designed for the preform transport channel. And drink or water filling machine need this ring on the bottles. PP, PC and PET material stretch rate is different, so the preform design for them are different.

• Preform mould structure

XS Plastic Mould always keep the mind that a good quality preform mould start from the mould design. So good preform mould strucutre is most important. All of XS Plastic Mould Co., Ltd engineers have been trained about the preform mould knowledge. We always keep the PET preform mould structure in our mind. Preform molds consists of the male core, the female cavity, and the neck inserts. The latter have to move during ejection of the part to release the undercuts created by the thread beads. For this purpose they are mounted on slides that are often cam-driven. Cores and cavities are always water cooled.

• Preform mould steel

Preform mold steel: S136, 2316, etc. Preform mold core inserts and sliders can be titanizing coasting to provide better surface finish. After titanizing, the surface will with golden colour. S136 and 2316 steel will be done vacuum quenching harding treatment. After harding treatment, the steel hardness can reach 48HRC to 52HRC. P20 steel used as the mold base. According customer’s request, some preform mold will use alloy brass to make strip plate to provide high efficient cooling.

• Preform plastic material

Usually there are three different plastic material can be used to produce preform: PET, PC, and PP. Due to different plastic material shrinkage rate is different. So preform mould shrinkage rate should be according the actual plastic material used to produce the preforms.

• Self-lock preform mould & normal preform mould

There are two type different structure on the preform mould — self-lock and non-self lock. We call non-self lock preform mold as normal preform mold.  Some clients have question that what the difference between self-lock and non-self lock. First, self-lock and non-self lock is about the structure on the mold parting which used to resist the mold shifting during injection molding. Self-lock preform mold each cavity insert and slider insert can resist the mold shifting. Please see below picture the area marked by red colour.

And non-self lock PET preform mold (normal PET preform mold) resist the mold parting shifting mold by A plate and slider blocks. Please see below picture the area marked by red colour.

Compare with normal preform mold, self-lock preform mold have longer life that preform neck without flash. So order self-lock PET preform mould or nonself-lock PET preform mould, should be according the quantity of the preforms.  In case, quantity of the preforms is small, then nonself-lock preform mould with less cavity no. fit for your needs. Otherwise self-lock preform mould with more cavity no. will be a better choose.

• Hot runner system for preform mould

There are two different types hot runner widely used for preform moulds – valve gated hot runner and thermally gated hot runner. This is an obvious difference on the preform mold profile.

Thermally gated hot runner use rod heaters and rod heaters were pluged into mold from one side to another side. In order to easily assemble and maintain heaters, often there is no cover on the mold heaters insert side. So we can see the heaters and wires from preform mold one side. Thermally gated hot runner temperature controller one zone control one rod heater. With this reason thermally gated hot runner temperature controller have less controller zones compare with valved gated hot runner temperature controller.

Valved gated hot runner use ring heaters and contain one manifold plate.  We only can see the hot runner socket on the mold. Valved gated hot runner preform every heater need to be controlled by sperated temperature controller zone. Compare with thermally gated hot runner temperature controller, valved gated hot runner temperature controller have more controller zones.

• Types of gate vestige

There are total three types of gate vestige for different hot runner gate preforms — long length vestige, short length vestige and flat little length vestige.

The vestige difference is caused by the different hot runner nozzle design. Long length vestige preform hot runner nozzel without heater or very little length heater.  So the gestige length is very long. Need to use preform gestige cutting machine to trim the preform, then can go on the strech blow molding with these preforms.

There are two ways to separate the hot melt coming through the hot run-
ner from the cooled preform: thermal and mechanical. Thermally gated hot
runners are most prevalent in one-stage while it is the other way around in
two-stage injection molding.
In a thermally gated hot runner the break point between the hot and cold
melts is controlled by temperature alone. As seen in above picture the tempera-ture difference between the cold cavity and the hot melt is substantial at around 255°C (491°F). A suitable insulation made from stainless steel or other material with insulating properties separates the two sections. When the machine ejects the preforms the melt breaks at the point where the
cold gate vestige connects with the hotter material inside the nozzle. This
material is already partly cooled down and so has a higher than melt vis-
cosity. This prevents it from seeping into the cavity or lead to “stringing,”
a common defect where small strands of PET from the melt stream are
pulled out with the preform during ejection. An air gap may also assist in
the separation process.

Valve-gated hot runners use a mechanical seal between the hot and
cold areas by means of a pin called the valve stem. Usually around 3 mm
(1/8 in.) to 5 mm (0.2 in.) in diameter, this pin moves back allowing melt
flow into the cavity, stays back during hold time, then moves forward con-
trolled by a timer that energizes with the end of hold time. Gate vestiges
made with valve-gated hot runners are on average shorter than with ther-
mally gated ones and the cut-off is more precise. Properly operated they
also tend to give less problems with stringing and gate crystallinity. Disad-
vantage of valve gates is the higher maintenance requirement for the pins
and the air cylinders driving them.

• Preform mould pictures made by XS Plastic Mould showing

• Preform mould test videos

Welcome to contact XS Plastic Mould Co., Ltd to develop preform moulds. We will do our best to provide you best quality preform moulds.

Preform mould knowleadge.

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This page is about the knowleadge of preform mould knowleadge.

1. The diference between neck 24/400, 24/410 and 24/415 on preforms.

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24 means approximately 24mm of the diameter across outside of the preform thread. 400, 410 and 410 are detail specifiation of the thread style.

24/400. This a very common neck style features a single thread that just slightly overlaps, and requires just a single rotation of the closure.

24/410. Ideal for taller styles of closures, this common neck style offers more height between the sholder of the bottle and the top of the threads. It also requires nearly two full turns of the closure in order to fully seal the package.

24/415. Prefect for pumps and sprayers, a 24-415 neck requires more than two full rotations fo fully apply the closure.

XS Plastic Mould Co., Ltd have long history in making stretch blow moulds for the semi-auto and full-auto stretch blow molding machine. Blow moulds play a large part in making high-quality bottles. While the machine has to deliver preforms at the right temperature, it is the blow moulds that give containers repeatable features and a brilliant appearance.

• Bottle design

Before stretch blow mould design, we need to make bottle design and confirm with client first.

XS Plastic Mould Co., Ltd provide both 2D and 3D bottle drawing. We make the drawing according client’s bottle sample or pictures. We can make the little change on the design according customer’s requirement.

• Strech blow mold design

Today’s mold-making process starts with a three-dimensional (3D) computer model of the container itself. Physical models may be made by a variety of processes, the most popular still being stereo lithography with 3D printing catching up quickly because of the availability of low-cost printers. The model may be used to give marketing people a better “feeling” for a new container. Once approved, data of the computer model are then fitted in a new or existing mold base. At this point, shrinkage has to be added to the container dimensions. Polyethylene terephthalate (PET) shrinks approximately 0.08% but shrinkage is not uniform and it is the experience of the mold maker that determines how closely the capacity of the container matches specification. A variety of computer-aided design (CAD)/ computer-aided manufacture (CAM) programs allow the creation of machine cutter paths that are downloaded directly into high-speed machining centers. Machine operators load and center blocks of aluminum of suitable size and special cutters, spinning at up to 30,000 r.p.m., move at a speed of up to 20 m/min. The resulting cavity surface is already smooth to the eye but most mold makers add a high, mirror-like polish, which still requires skilled, manual labor. The use of sandblasted surfaces that are common in other plastic processes has gained some ground as there is little difference in the appearance of the containers. Some mold makers then coat the cavity surfaces with various materials, often containing nickel and Teflon, to give it abrasion resistance.

Neck and thread finish are already formed in the preform; so blow molds form only the body and base of the bottle. In the reheat stretch blow molding (RSBM) process they consist of three parts: two mold halves and one base insert (also called push-up). The base insert is necessary because the walls at the base of the concave container could not slide over the mold halves during mold opening if these were forming them. Instead, the verti-cally moving base insert is drawn out of the way before, or as, the mold opens. While the three-piece design is common to all molds, they are manu-factured quite differently depending on the type of machine to which they will be fitted. Linear machines have all mold cavities mounted within two blocks where the cavities sit side by side. In rotary machines each blow mold is mounted to a separate carrier, opening and closing individu-ally. Modern machines use so-called shell molds whereby the actual mold halves are only 5-mm thick and are assembled onto bases that are all the same for a family of containers. These bases carry all water connections and need not be touched during a changeover, thus reducing valuable time.

• Stretch blow mould material

Normally use Aluminum 7075, steel P20 or steel C45 to make the stretch blow moulds.  Quality and price 7075 > P20 > C45. Base inserts may be of the same material or made from beryllium–copper. Aluminum 7075 especial high heat
transfer rate, easy machinability, and lightweight. Most of the full automatical stretch blow molding machine moulds widely use aluminum 7075 to make the moulds.

• Venting

Venting is another area where the experience of the mold maker becomes extremely important. Because PET fills the mold cavity during blowing, the air inside the cavity must be exhausted. For this purpose mold makers add a variety of vents. Compared to other processes, such as injection molding or extrusion blow molding, PET is processed at a relatively low temperature in the RSBM process. Vent sizes are limited to 0.04 mm (0.0015 in.) in injection molding but vents of up to 0.5 mm (0.020 in.) are used in RSBM with hole vents up to 1 mm (0.040 in.). All molds have vents on the contact surface of the cavities. One mold half is typically completely recessed against the mold base by up to 0.20 mm (0.08 in.) or more commonly by 0.15 mm (0.006 in.). Base vents are also common and are accomplished by leaving the base insert to move 0.25–0.3 mm (0.010–0.012 in.) downward under the force of the stretch rod. The resulting ring-shaped gap between base insert and mold cavity allows air to escape. Hole vents up to 1 mm are used in areas where air entrapment is suspected. Vents of this diameter may not show in areas where the material has stretched and consequentially strain-hardened but will show as small dimples where this is not the case. A common example of highly stretched material is the foot of a petaloid base for carbonated soft drinks (CSD) containers. Two small holes in each foot let air escape that might otherwise be trapped by the material flowing around it.  Another use of venting is to direct PET into hard-to-blow areas. In a highly oval bottle, for example, there is always the possibility of a ridge of higher wall thickness forming at the center of the narrow side of the container. Vent holes at the far side of the mold can attract PET to flow more quickly into these areas, thereby stretching out the preform walls close to the narrow side. A fine sandblast finish instead of the mirror-finish also helps to let the air move out of the mold. Due to low temperature in the RSBM process compared with uses in other processes, PET does not flow easily into small mold crevices. Minimum dimensions for female radii might be given as 0.8 mm (1/32 in.) but it will depend on the stretch ratio of the PET flowing toward it whether it will fill out or form a greater radius instead. Male radii should be double that amount especially when used in bases. Here a sharp radius may cause a crease in the material and open the door to stress cracking. Venting in these areas can be attempted to reduce the risk of air entrapment stopping the advance of the parison but more often than not they do not seem to have much effect. We will simply have to live with the fact that PET benefits from more generous radii in this process.

• Stretch blow mold pictures

• Stretch blow mould test video

• Stretch blow mould for full automatic stretch blow moulding machine in our workshop.

In this pag, we will go over the most common processing problems found in RSBM. There is often more than one possible cause—and more than one solution to a particular problem even from the same cause. Not all machines have the features that may be mentioned from time to time, so other solutions may have to be found. Because solutions in single stage are often quite different than in two stage, they are added to the end of the discussion.

• Internal Folding in the Neck Area

A number of processors with older machines have this problem, which usually shows up as ring of thick material at the start of the bottle shoulder.

Causes

1. Insufficient heat in the area underneath the NSR.
2. Preblow pressure too late or too low.

Solutions

1. Increase heat in zone #1. If that leads to overheating and haze, increase fan cooling.
2. Move oven bank slightly lower.
3. Push lamp #1 closer to the preform.
4. Reduce heat in weak areas especially the base. This strengthens these areas of the preform allowing more material to be pulled out of the neck.
5. Reduce preblow pressure delay in combination with.
6. Increase preblow pressure: while proceeding in this way, occasionally turn high-pressure off, ensuring that the preblow pressure is not creating too big a bubble.

• Excessive Material in the Base of the Bottle “Candle Stick”

This defect consists of unsightly accumulations of material in a ring or half-ring shape around the inside center of the bottle. External base folding has the same causes and solutions.

Causes

1. Preblow pressure too late or too low: Material is allowed to gather around the stretch rod, cooling down as a result, and becoming too cold and thick to blow out during high pressure blow.
2. Preform base too hot.
3. Combination of blow pressure too low and base too hot.

Solutions

1. Increase preblow pressure: While proceeding in this way, occasionally turn high-pressure off, ensuring that the preblow pressure is not creating too big a bubble.
2. Decrease preblow delay: If the delay is already at zero it might indicate that the preblow valve is opening late. Try replacing it.
3. Move the switch indicating the end position of the stretch rod away from the bottle base until the gate goes off-center, then move it back a little. It may be taking too long for the high-pressure air to reach the bottom of the preform.
4. Decrease heat to the base of the preform.
5. Increase blow pressure to a maximum of 40 bar (580 psi).

• Off-Center Gate

Whenever the preform gate is not exactly in the center of the bottle base, the wall thickness of the bottle becomes uneven (Fig. 10.10). If for example, the stretch rod tip is skewed to the left, the material on the left will reach the mold wall earlier and more material will harden there even with a perfect temperature profile around the circumference of the preform.

Causes

1. Preblow pressure too high: This pressure can become high enough to blow the preform off the stretch rod. Minute temperature differences around the circumference of the preform drive the preform toward the cooler side.
2. Preblow pressure too early: If preblow pressure commences before the stretch rod is firmly engaged in the preform bottom, the gate may wander off the center.
3. High-pressure air too early: The switch indicating the end position of the stretch rod may be not close enough.
4. Stretch rod incorrectly set: Stretch rods should be 1/2–1 mm (0.020–0.040in.) higher from the base insert than the preform gate wall thickness. As that distance increases, the preform may slip to one side.
5. Stretch rod bent: As neck finishes become smaller, as is often the case for custom containers, stretch rods have to be smaller too. The smaller in diameter they become the easier they bend when they hit a cold preform, for example. This is easy to see: the gate will always be skewed to the same side. Check several bottles and see where the gate is in relation to the recycling symbol or some other engraving. Other causes will push the gate randomly.
6. Preform intrinsic viscosity (IV) too low: When preforms are underdried or overheated during injection their IV may drop significantly and they may blow off the stretch rod.

Solutions

1. reduce preblow pressure,
2. increase preblow pressure delay,
3. move stretch rod switch closer to end of stretch rod or increase blow delay,
4. readjust stretch rod,
5. take stretch rod out and roll over a plane surface. This will show any distortion, and
6. try preforms from a different gaylord or batch. Check IV if necessary.

• Haze in Bottle Walls

Cloudiness or haze first shows when temperature induced crystallinity reaches around 3%. It should not be confused with gate crystallinity, which is always a preform defect whereas haze can be created in both injection and blow molding. Whitish rings or streaks right around the preform gate indicate gate crystallinity whereas haze can occur anywhere on the preform, with prevalence toward the bottom. Haze usually shows as a milky coating on the outside of the bottle.

Causes

1. Haziness already present in the preform: It is not unusual to
   see these defects in preforms.
2. Preform overheats in the blow machine oven: When preform temperature comes close to 120°C (248°F) preforms may crystallize during equalization as they cool down.
3. Mold temperature may be above 65°C (149°F).
4. If haze happens randomly and is not found in the preforms, preforms with a higher initial temperature may have become mixed with the colder ones for which the process was adjusted.

Solutions

1. check preform supply first
2. reduce lamp settings, increase fan cooling, or speed up machine
3. reduce mold temperature to 60°C (140°F) or less
4. ensure all preforms are at the same initial temperature

• Pearlescence or Stress Whitening

Also referred to as stress whitening, this defect shows up as whitish rings not unlike pearls, hence the name. They are actually microcracks in the PET molecule structure. They are always on the inside of the bottle and show as a milky coating. If there is doubt whether whitening observed in the bottle is haze or pearlescence a simple test can be done: if the affected areas can be scratched off with a finger nail on the inside of the bottle, it is always pearlescence. This can be understood from the knowledge that the inside of the preform has to stretch further and therefore also breaks first.

Causes

1. Preforms are overstretched during blowing. They are either too cold or too thin. The difference can be determined by checking the wall thickness of the affected areas. If they are very thin, the preform may be too hot in this area while other areas are too cold. In this case lamps pointing at the pearlescent part(s) may be at too high a setting. If the affected area is of normal or above normal thickness the preform was too cold before blowing.
2. Preforms are too cold overall.
3. If pearlescence happens randomly preforms with a lower initial temperature may have become mixed with the warmer ones for which the process was adjusted.

Solution

1. Reduce relevant lamp settings to areas that are too thin while at the same time increase lamp setting to areas adjacent to the affect areas. This will move material into the overstretch parts of the bottle leading to thicker walls.
2. Increase overall lamp settings if wall distribution is acceptable.
3. Ensure all preforms are at the same initial temperature.
4. Reduce fan cooling and thus increasing oven temperature often does not lead to success as this measure mostly effects the outside preform wall.

In case get other troubleshooting, welcome to contact XS Plastic Mould, we will study and offer solution.

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We are looking forward to hearing from you. Please feel free to get in touch via the contact information below, we will get back to you as soon as possible.

XS Plastic Mould Co., Ltd.

Tel.:+86-576-84407662.

Mobile: +86-13251068920 (whatsapp & wechat)

Email:  sales@xsplasticmould.com

Address: Huangyan, Taizhou City, Zhejiang Province, China